How Muscles Work: Contraction

By: Sarah Johnson

Summary

The first of a three part series on how your muscles work.
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​So you’ve decided to embark on this whole fitness journey, get healthy, and change your life. Right on and welcome friend. If you’re new to working out there are a few pieces of advice I would like to give you, but instead of giving you fitness tips you’ve probably heard before, I’ll save it and just say this: question everything.

Questioning means you want to learn, and when it comes to changing your life and getting healthy, you want to do what’s best for YOU. Don’t believe everything you see, do your own research, and question everything.

You need to learn how your body is moving, working, and performing. The more you understand the science behind it, the more likely you are to be successful. The body is a cool machine that can do A LOT and I mean A LOT (like holy cow women can produce tiny humans?)

You might have a few goals like lose a little body fat and build some lean, sexy muscle, but have you ever stopped and wondered how the body actually accomplishes these things? Well if you have you’re in luck, because today I’m breaking out some nerdom and teaching you the basics of how muscles work.

Types of Muscle

Did you know there are three different types of muscle fibers? These include cardiac (in the heart), smooth (think organs like stomach and bladder), and skeletal muscle. The last of these is what we’ll be focusing on as this is the one that we want to shape and is also the one in charge of moving bones and the body. It starts with muscle contraction.

Contraction

So when it comes to the muscle actually contracting (flexing) and putting in work, here’s what happens (you might want to put your thinking cap on for this):

Electrical impulses (called action potentials) are sent from your nervous system down the axon of the neuron to relay this message.

Once these action potentials reach the end of the axon, chemical messengers referred to as neurotransmitters are released. These neurotransmitters cross the
the gap between the neuron and the muscle fiber (called the synapse) to relay the message to said muscle fiber.

Receptor sites on the muscle fiber receive these neurotransmitters.
(This is where it gets tricky!)

The neurotransmitter used by the neuromuscular system (Acetylcholine), then stimulates the muscle fibers to release calcium into the sarcoplasm, which is the outer covering of the muscle fiber and also where some glycogen is stored (think energy for muscles)

If I haven’t lost you yet, the next step is for calcium to bind to troponin, forcing tropomyosin to detach from the myosin binding site and allowing myosin to attach to actin.

​This causes the filaments, myosin and actin, to pull across each other and the muscle to shorten or flex. Check out the pictures below to help.

Your nervous system signals your muscles when to contract.

When myosin and actin attach and pull across each other to shorten (contract) the muscle.

All of this might have just sounded foreign to you, but it comes down to this: it all starts with the nervous system telling your body to move. From there, chemical messengers are sent to your muscles from your nervous system and once those chemical messengers are in place, velcro like structures in the muscles pull across each other to contract and shorten. Ta-Da!

I don’t want to bombard you with all of this at once, so I have decided to break up “How Muscles Work” into bite-sized segments. Next week I’ll talk about how these awesome muscles are actually broken down in the gym and then repaired in our rest time to build that strong, lean look you’re looking for.

Thanks for reading and being curious as to how this whole building muscle thing works. We write to help you learn because knowledge (I had to say it) is power! So keep on reading the artices from the other fellow nerdy trainers and fitness professionals and look out for more to come from me and my Indy Fitness Mag Family!